There is nobody, in the commonwealth of learning, who does not profess himself a lover of truth, — and there is not a rational creature, that would not take it amiss, to be thought otherwise of. And yet, for all this, one may truly say, there are very few lovers of truth, for truth-sake, even amongst those who persuade themselves that they are so. How a man may know, whether he be so, in earnest, is worth inquiry; and I think, there is this one unerring mark of it, viz. the not entertaining any proposition with greater assurance than the proofs it is built on will warrant. Whoever goes beyond this measure of assent, it is plain, receives not truth in the love of it, loves not truth for truth-sake, but for some other by-end.

John Locke (1632-1704) English philosopher

An Essay Concerning Human Understanding, Book 4 “Of Knowledge and Opinion,” ch. 19 “Of Enthusiasm,” sec. 1 “Love of truth necessary” (1689)
    (Source)